Thermoplastic Polyurethane With Reduced Tendency To Bloom

ABSTRACT

The present invention discloses a thermoplastic polyurethane which is comprised of the reaction product of (1) a hydroxyl terminated polyester intermediate, (2) a polyisocyanate, and (3) a glycol chain extender; wherein the hydroxyl terminated polyester intermediate is comprised of repeat units that are derived from 1,3-propylene glycol and a dicarboxylic acid; wherein the hydroxyl terminated polyester intermediate has a number average molecular weight from 500 to 10,000; and wherein the thermoplastic polyurethane includes hard segments that are the reaction product of the polyisocyanate and the glycol chain extender. This thermoplastic polyurethane is unique in that it has a greatly reduced tendency to bloom. This is highly desirable in applications where high clarity is desired because blooming causes articles containing the thermoplastic polyurethane to be hazy or foggy in appearance. Blooming can also reduce the ability of an article made with the thermoplastic polyurethane to be securely bound to another article with an adhesive.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Provisional Application Ser. No.61/161,162 filed on Mar. 18, 2009.

FIELD OF THE INVENTION

The present invention relates to thermoplastic polyurethanes (TPUs) thatoffer reduced blooming characteristics. These thermoplastic polyurethaneare comprised of the reaction product of (1) a hydroxyl terminatedpolyester intermediate, (2) a polyisocyanate, and (3) a glycol chainextender; wherein the hydroxyl terminated polyester intermediate iscomprised of repeat units that are derived from 1,3-propylene glycol anda dicarboxylic acid; wherein the hydroxyl terminated polyesterintermediate has a number average molecular weight which is within therange of 500 to 10,000 Daltons; and wherein the thermoplasticpolyurethane includes hard segments that are the reaction product of thepolyisocyanate and the glycol chain extender.

BACKGROUND OF THE INVENTION

TPU polymers are typically made by reacting (1) a hydroxyl terminatedpolyether or hydroxyl terminated polyester, (2) a chain extender, and(3) an isocyanate compound. Various types of compounds for each of thethree reactants are disclosed in the literature. The TPU polymers madefrom these three reactants find use in various fields where products aremade by melt processing the TPU and forming it into various shapes toproduce desired articles by processes such as extrusion and molding.

TPUs are segmented polymers having soft segments and hard segments. Thisfeature accounts for their excellent elastic properties. The softsegments are derived from the hydroxyl terminated polyether or polyesterand the hard segments are derived from the isocyanate and the chainextender. The chain extender is typically one of a variety of glycols,such as 1,4-butane glycol.

U.S. Pat. No. 5,959,059 discloses a TPU made from a hydroxyl terminatedpolyether, a glycol chain extender, and a diisocyanate. This TPU isdescribed as being useful for making fibers, golf ball cores,recreational wheels, and other uses.

Blooming is a problem that is frequently observed in articles made withthermoplastic polyurethanes. Blooming is something also referred to as“surface haze” or “surface fogging.” Blooming is undesirable because itcan destroy the aesthetic surface characteristics of articles made withpolymers that bloom. It is particularly undesirable for bloom to occurin articles where clarity is desired. Bloom is also undesirable becauseit can reduce the ability of an article made with the blooming polymerto be securely bound to other article with adhesives. Blooming has longbeen recognized as serious problem in some applications and an effectivemeans for alleviating it as been sought for years.

U.S. Pat. No. 5,491,211 discloses a thermoplastic polyurethanecomposition that is reported to be bloom-free. This objective isreported to be accomplished by including a monofunctional compound thatis reactive with isocyanates in the thermoplastic polyurethanecomposition. U.S. Pat. No. 5,491,211 specifically discloses the use ofmonofunctional alcohols that contain at least 14 carbon atoms, such as1-tetradecanol, 1-octadecanol, or 1-docosanol, for the purpose ofcontrolling bloom.

SUMMARY OF THE INVENTION

The subject invention relates to a thermoplastic polyurethane that has agreatly reduced tendency to bloom. Reducing the tendency of a polymer tobloom is highly desirable in applications where high clarity is desiredbecause blooming causes articles made with polymers that bloom to behazy or foggy in appearance. Blooming can also reduce the ability of anarticle made with the polymer that blooms to be securely bound toanother article with an adhesive.

The present invention discloses a thermoplastic polyurethane which iscomprised of the reaction product of (1) a hydroxyl terminated polyesterintermediate, (2) a polyisocyanate, and (3) a glycol chain extender;wherein the hydroxyl terminated polyester intermediate is comprised ofrepeat units that are derived from 1,3-propylene glycol and adicarboxylic acid; wherein the hydroxyl terminated polyesterintermediate has a number average molecular weight which is within therange of 500 to 10,000 Daltons; and wherein the thermoplasticpolyurethane includes hard segments that are the reaction product of thepolyisocyanate and the glycol chain extender. The thermoplasticpolyurethane compositions of this invention do not require amonofunctional compound that is reactive with isocyanates, such asmonofunctional alkylene alcohols having at least 14 carbon atoms, tocontrol bloom.

The present invention further discloses a process for manufacturing amolded article which comprises (a) heating a thermoplastic polyurethanecomposition to a temperature which is above the melting point of thethermoplastic polyurethane composition, wherein the thermoplasticpolyurethane composition is the reaction product of (1) a hydroxylterminated polyester intermediate, (2) a polyisocyanate, and (3) aglycol chain extender; wherein the hydroxyl terminated polyesterintermediate is comprised of repeat units that are derived from1,3-propylene glycol and a dicarboxylic acid; wherein the hydroxylterminated polyester intermediate has a number average molecular weightwhich is within the range of 500 to 10,000 Daltons; and wherein thethermoplastic polyurethane includes hard segments that are the reactionproduct of the polyisocyanate and the glycol chain extender; (b)injecting the thermoplastic polyurethane composition into a mold; (c)cooling the thermoplastic polyurethane composition in the mold to atemperature which is below the melting point of the thermoplasticpolyurethane composition to produce the molded article; and (d) removingthe molded article from the mold.

The present invention further discloses a process for manufacturingextruded articles, such as fibers, sheets, films, tubes and hoses, whichcomprises (a) heating a thermoplastic polyurethane composition to atemperature which is above the melting point of the thermoplasticpolyurethane composition, wherein the thermoplastic polyurethanecomposition is the reaction product of (1) a hydroxyl terminatedpolyester intermediate, (2) a polyisocyanate, and (3) a glycol chainextender; wherein the hydroxyl terminated polyester intermediate iscomprised of repeat units that are derived from 1,3-propylene glycol anda dicarboxylic acid; wherein the hydroxyl terminated polyesterintermediate has a number average molecular weight which is within therange of 500 to 10,000 Daltons; and wherein the thermoplasticpolyurethane includes hard segments that are the reaction product of thepolyisocyanate and the glycol chain extender; (b) extruding thethermoplastic polyurethane composition into the desired shape of theextruded article; and (c) cooling the thermoplastic polyurethanecomposition to a temperature which is below the melting point of thethermoplastic polyurethane composition to produce the extruded article.Such an extrusion process is of particular value in manufacturing cleartubes and hoses for conveying vegetable oils, other edible liquids, andother organic liquids. The extrusion process can be a profile extrusionprocess.

In another embodiment of this invention the thermoplastic polyurethanecomposition can be blow molded into a desired article of manufacture.For instance, the polyurethane composition can be blow molded into clearbottles.

In another embodiment of this invention a shoe having an upper and asole is disclosed. In this shoe the sole is comprised of a thermoplasticpolyurethane composition which is the reaction product of (1) a hydroxylterminated polyester intermediate, (2) a polyisocyanate, and (3) aglycol chain extender; wherein the hydroxyl terminated polyesterintermediate is comprised of repeat units that are derived from1,3-propylene glycol and a dicarboxylic acid; wherein the hydroxylterminated polyester intermediate has a number average molecular weightwhich is within the range of 500 to 10,000 Daltons; and wherein thethermoplastic polyurethane includes hard segments that are the reactionproduct of the polyisocyanate and the glycol chain extender.

DETAILED DESCRIPTION OF THE INVENTION

The thermoplastic polyurethane of this invention is the reaction productof (1) a hydroxyl terminated polyester intermediate, (2) apolyisocyanate, and (3) a glycol chain extender. The technique underwhich these reactants are polymerized to synthesize the thermoplasticpolyurethane is conducted utilizing conventional equipment, catalysts,and procedures. However, it is important for the hydroxyl terminatedpolyester intermediate to be comprised of repeat units that are derivedfrom 1,3-propylene glycol and a dicarboxylic acid. The hydroxylterminated polyester intermediate will also typically have a numberaverage molecular weight which is within the range of 500 to 10,000Daltons.

The hydroxyl terminated intermediate used in making the thermoplasticpolyurethane is a hydroxyl terminated polyester intermediate that iscomprised of repeat units that are derived from 1,3-propane glycol and adicarboxylic acid. The 1,3-propane glycol will represent at least 70weight percent of the glycol component used in synthesizing the hydroxylterminated polyester intermediate. Typically, the 1,3-propane glycolwill represent at least 80 eight percent of the glycol component used insynthesizing the hydroxyl terminated polyester intermediate and willpreferably represent at least 90 weight percent of the glycol component.It is normally more preferred for the 1,3-propane glycol to represent atleast 95 weight percent of the glycol component used in synthesizing thehydroxyl terminated polyester intermediate.

The dicarboxylic acids used in making the hydroxyl terminated polyesterintermediate can be aliphatic, cycloaliphatic, aromatic, or combinationsthereof. Suitable dicarboxylic acids which may be used alone or inmixtures generally have a total of from 4 to 15 carbon atoms andinclude: succinic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, phthalicacid, isophthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylicacid, cyclohexane dicarboxylic acid, and the like. The dicarboxylic acidused will typically be of the formula: HOOC(CH₂)_(n)COOH, wherein nrepresents an integer within the range of 2 to 10, preferably from 4 to8, and most preferably 4-7. Adipic acid is a preferred acid. Anhydridesof the above dicarboxylic acids, such as phthalic anhydride,tetrahydrophthalic anhydride, or the like, can also be used tosynthesize the intermediate by a transesterification reaction.

The hydroxyl terminated polyester intermediate used in making thethermoplastic polyurethanes of this invention will typically have anumber average molecular weight (Mn), as determined by assay of theterminal functional groups, which is within the range of about 500 toabout 10,000 Daltons, typically about 750 to about 4,000 Daltons,desirably from about 1000 to about 3,000 Daltons, most preferably fromabout 1000 to about 2,500 Daltons. A blend of two or more hydroxylterminated polyester intermediates may be used to make the TPU of thisinvention.

The glycol chain extender used in making the thermoplastic polyurethaneof this invention is either ethylene glycol, propylene glycol or amixture thereof. The glycol chain extender can also include 1,4-butaneglycol, 1,5-pentane diol, 1,6-hexane diol, and hydroquinone his(2-hydroxyethyl)ether (HQEE). It is highly preferred to utilize only1,3-propane diol and/or 1,4-butane diol as the chain extender.

The polyisocyanate used in synthesizing the thermoplastic polyurethaneis preferably a diisocyanate. While aliphatic diisocyanates can beutilized, aromatic diisocyanates are highly preferred. Moreover, the useof multifunctional isocyanate compounds, i.e., triisocyanates, etc.,which cause crosslinking, are generally avoided and thus the amountused, if any, is generally less than 4 mole percent and preferably lessthan 2 mole percent based upon the total moles of all of the variousisocyanates used. Suitable diisocyanates include aromatic diisocyanates,such as, 4,4′-methylenebis-(phenyl isocyanate) (MDI),2,4′-methylenebis-(phenyl isocyanate), m-xylylene diisocyanate (XDI),m-tetramethyl xylylene diisocyanate (TMXDI), phenylene-1,4-diisocyanate(PPDI), 1,5-naphthalene diisocyanate (NDI),diphenylmethane-3,3′-dimethoxy-4,4′-diisocyanate (TODI), and toluenediisocyanate (TDI). Examples of suitable aliphatic diisocyanates includeisophorone diisocyanate (IPDI), 1,4-cyclohexyl diisocyanate (CHDI),hexamethylene diisocyanate (HDI), 1,6-diisocyanato-2,2,4,4-tetramethylhexane (TMDI), 1,3-bis(isocyanato-methyl)cyclohexane (HXDI), 1,6-hexanediisocyanate (HDI), 1,10-decane diisocyanate, andtrans-dicyclohexylmethane diisocyanate (HMDI). A commonly useddiisocyanate is 4,4′-methylenebis(phenyl isocyanate) (MDI). Dimers andtrimers of the above diisocyanates may also be used as well as a blendof two or more diisocyanates may be used.

The polyisocyanate used in this invention may be in the form of a lowmolecular weight polymer or oligomer which is end capped with anisocyanate. For example, the hydroxyl terminated polyester intermediatedescribed above may be reacted with an isocyanate-containing compound tocreate a low molecular weight polymer end capped with isocyanate. In theTPU art, such materials are normally referred to as pre-polymers. Suchpre-polymers normally have a number average molecular weight (Mn) whichis within the range of about 500 to about 10,000 Daltons.

The mole ratio of the one or more diisocyanates is generally from about0.95 to about 1.05, and preferably from about 0.98 to about 1.03 molesper mole of the total moles of the one or more hydroxyl terminatedpolyester intermediates and the one or more chain extenders.

The process to produce the TPU polymer of this invention can utilizeconventional TPU manufacturing equipment. The hydroxyl terminatedpolyester intermediate, the diisocyanate, and the chain extender, asnoted above, are generally added together and reacted in accordance withany conventional urethane reaction method. Preferably, the TPU formingcomponents of the present invention are melt polymerized in a suitablemixer, such as an internal mixer known as a Banbury mixer, or preferablyan extruder. In the preferred process, the hydroxyl terminated polyesterintermediate is blended with the glycol chain extender and added to theextruder as a blend. The diisocyanate is added separately to theextruder. Suitable processing or polymerization starting temperatures ofthe diisocyanate is from about 100° C. to about 200° C., and preferablyfrom about 100° C. to about 150° C. Suitable processing orpolymerization starting temperatures of the blend of the hydroxylterminated polyester intermediate and the chain extender is from about100° C. to about 220° C., and preferably from about 150° C. to 200° C.Suitable mixing times in order to enable the various components to reactand form the TPU polymers of the present invention are generally fromabout 2 to about 10 minutes, and preferably from about 3 to about 5minutes.

The preferred process to produce the TPU of this invention is theprocess referred to as the one-shot polymerization process. In theone-shot polymerization process which generally occurs in situ, asimultaneous reaction occurs between three components, that is the oneor more hydroxyl terminated polyester intermediates, the glycol, and thediisocyanate. The reaction is generally initiated at a temperature offrom about 90° C. to about 120° C. Inasmuch as the reaction isexothermic, the reaction temperature generally increases to about 220°C. to 250° C. In cases where ethylene glycol is used as the chainextender, it is important to limit the temperature of this exothermicreaction to a maximum of 235° C. to prevent undesired levels of foamformation. The TPU polymer will exit the reaction extruder and bepelletized. The pellets of TPU are normally stored in a heated vessel tocontinue the reaction and to dry the TPU pellets.

It is often desirable to utilize catalysts such as stannous and othermetal carboxylates as well as tertiary amines. Examples of metalcarboxylates catalysts include stannous octoate, dibutyl tin dilaurate,phenyl mercuric propionate, lead octoate, iron acetylacetonate,magnesium acetylacetonate, and the like. Examples of tertiary aminecatalysts include triethylene diamine, and the like. The amount of theone or more catalysts is low, generally from about 50 to about 100 partsby weight per million parts by weight of the end TPU polymer formed.

The weight average molecular weight (Mw) of the TPU polymer of thepresent invention range from about 90,000 to about 600,000 Daltons,preferably from about 100,000 to about 300,000 Daltons, and morepreferably from about 120,000 to about 250,000 Daltons. The Mw of theTPU polymer is measured according to gel permeation chromatography (GPC)against polystyrene standard.

When a higher molecular weight TPU polymer is desired, it can beachieved by using a small amount of a cross linking agent having anaverage functionality greater than 2.0 to induce cross linking. Theamount of cross linking agent used is preferably less than 2 molepercent of the total moles of chain extender, and more preferably lessthan 1 mole percent. A particularly desirable method to increase themolecular weight in the preferred TPU polymer is to replace less than 1mole percent of the chain extender with trimethylol propane (TMP).

The cross linking is accomplished by adding a cross linking agent havingan average functionality greater than 2.0 together with the hydroxylterminated intermediate, the isocyanate compound, and chain extender inthe reaction mixture to manufacture the TPU polymer. The amount of crosslinking agent used in the reaction mixture to make the TPU polymer willdepend on the desired molecular weight and the effectiveness of theparticular cross linking agent used. Usually, less than 2.0 molepercent, and preferably less than 1.0 mole percent, based on the totalmoles of chain extender used in making the TPU polymer are used. Levelsof cross linking agent greater than 2.0 mole percent, based on the totalmoles of chain extender would be difficult to melt process. Therefore,the level of cross linking agent used is from about 0.05 mole percent toabout 2.0 mole percent based on the total moles of hydroxyl components.

The cross linking agents can be any monomeric or oligomeric materialswhich have an average functionality of greater than 2.0 and have theability to cross link the TPU polymer. Such materials are well known inthe art of thermoset polyurethanes. Preferred cross linking agentsinclude trimethylol propane (TMP) and pentaerythritol. Trimethylolpropane has been found to particularly be a desirable cross linkingagent.

The TPU polymers of the present invention can be mixed with variousconventional additives or compounding agents, such as fillers,extenders, pigments, lubricants, UV absorbers, and the like. However,the TPUs of this invention are normally free of plasticizers. Fillersthat can be used include talc, silicates, clays, calcium carbonate, andthe like. The level of conventional additives will depend on the finalproperties and cost of the desired end-use application, as is well knownto those skilled in the art of compounding TPUs. The additives may beadded during the reaction to form the TPU, but are normally added in asecond compounding step.

The TPU polymer of this invention has a high melting point of at leastabout 170° C., preferably at least about 185° C., and most preferably atleast about 200° C. The TPUs of this invention will typically have amelt point which is within the range of 170° C. to 240° C., and willmore typically have a melting point which is within the range of 185° C.to 220° C. The TPUs of this invention will preferably have a meltingpoint which is within the range of 200° C. to 220° C. A high meltingpoint is important in applications using melt spun fibers with othersynthetic fibers, such as polyester. Certain melt coating applicationsalso require a high melting point TPU to withstand the manufacturingprocess, especially those applications which require the use offluorinated polymers. The melting point of the TPU polymer can bemeasured according to ASTM D-3417-99 using a differential scanningcalorimeter (DSC). However, in the case of very soft polymers theKopfler method can be used to measure the melting point of the TPU.

The hardness of the TPU polymers of this invention can range from beingextremely soft (Shore A hardness of about 20) to relatively hard (ShoreD hardness of about 80) as measured in accordance with ASTM D2240. TheTPU polymers of this invention will typically have a Shore A hardnesswhich is within the range of 30 to 70 and will more typically have aShore A hardness which is within the range of 35 to 60. The TPU can bemade softer by including a plasticizer, such as a phthalate plasticizerin the TPU composition. However, care should be taken to preclude theuse of plasticizers that compromise clarity in applications where it isdesirable for the product to be clear.

Other conventional additives can be included in the TPU compositions ofthis invention. Among these other conventional additives are, forexample, antioxidants, antiozone agents, antihydrolysis agents,extrusion aids, UV stabilizers, chain terminators, light stabilizers,colorants, and flame retardants. These additives and their use inpolyurethane compositions are generally known. Typically, theseadditives are used in amounts that achieve a desired effect. Excessiveamounts of additives may reduce other properties of the polyurethanecomposition beyond desired limits.

Antioxidants typically prevent or terminate oxidation reactions thatresult in degradation of the polyurethane article over the lifetime ofthe article. Typical antioxidants include ketones, aldehydes, and arylamines, as well as phenolic compounds. Specific examples of compoundsincludeethylenebis(oxyethylene)bis(3-t-butyl-4-hydroxy-5-methylcinnamate andtetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane.Examples of suitable commercial antioxidants include Irganox 1010,Irganox 1098, Irganox 565, and Irganox 1035 (Ciba-Geigy Corp., Ardsley,N.Y.).

Antiozone agents prevent or reduce damage caused by ozone andantihydrolysis agents prevent or reduce damage by water and otherhydrolyzing compounds. Examples of suitable antiozonants includep-phenylenediamine derivatives. Antihydrolysis agents include, forexample, Stabaxol P and Stabaxol P-200 (Rhein Chemie, Trenton, N.J.).

Extrusion aids facilitate movement of the polyurethane through theextruder. Waxes, such as Wax E (Hoechst-Celanese Corp., Chatham, N.J.),Acrawax (Lonza Inc., Fair Lawn, N.J.) and oxidized polyethylene 629A(Allied-Signal Inc., Morristown, N.J.), are suitable extrusion aids.These extrusion aids can also act as mold-release agents or additionalmold release agents can be added to the composition.

Chain terminators are used to control molecular weight. Examples ofchain terminators include monoalcohol compounds having 8 or more carbonatoms.

Light stabilizers prevent or reduce degradation of a polymer product dueto visible or ultraviolet light. Examples of suitable light stabilizersinclude benzotriazole, such as Tinuvin P, and hindered amine lightstabilizers, such as Tinuvin 770.

This invention is illustrated by the following examples that are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

Example 1 and Comparative Example 2

The TPUs made in this experiment were all made using the same generalprocedure. The procedure used involved heating a blend of hydroxylterminated polyester intermediate, chain extender, and diisocyanateseparately to about 150° C. and then mixing the ingredients. Thereactions were exothermic and the temperature increased to within therange of about 200° C. to 250° C. in about 1 to 5 minutes, during whichtime polymerization took place as evidenced by an increase in viscosity.The hydroxyl terminated intermediate used in making the TPU in Example 1was poly(1,3-propylene adipate) glycol and the hydroxyl terminatedintermediate used in Comparative Example 2 was poly(1,4-butyleneadipate) glycol. The chain extender used in making both polymers was1,4-butane diol and the diisocyanate used in making both polymers was4,4′-methylene bis-(phenyl isocyanate).

The thermoplastic polyurethane made in both Example 1 and ComparativeExample 2 was extruded into sheets. The sheets were aged for a period ofabout 4 years. The sheet made in Example 1 was essentially bloom-free.However, the sheet made in Comparative Example 2 exhibited severe bloom.In fact, bloom was removed from the sheet made in Comparative Example 2by rubbing the sheet with a fingertip. In any case, this experimentshows that bloom was essentially eliminated by utilizingpoly(1,3-propylene adipate) glycol as the hydroxyl terminated polyesterintermediate.

Examples 3-5 and Comparative Examples 6-7

The TPUs made in this series of experiments were all made using the samegeneral procedure. The procedure used involved heating a blend ofhydroxyl terminated polyester intermediate, chain extender, anddiisocyanate separately to about 150° C. and then mixing theingredients. The reactions were exothermic and the temperature increasedto within the range of about 200° C. to 250° C. in about 1 to 5 minutes,during which time polymerization took place as evidenced by an increasein viscosity. The polyol and chain extender utilized in synthesizingthese TPUs are identified in Table 1.

TABLE 1 Example 3 4 5 6 7 Polyol PDOA PDOA PDOA BDOA BDOA Chain ExtenderBDO BDO PDO BDO BDO Shore A Hardness 79 85 86 75 85 (ASTMD2240) TearStrength at Break 6100 7600 7500 5500 7000 (PSI)¹ Elongation (ASTM 510%540% 555% 680% 550% D412) Trouser Tear Strength 105 135 165 100 130(lb/in)² Bloom after 1 month none none none medium slight Bloom after 3months none none none heavy medium Bloom after 9 months none none none —— ¹ASTM D412 ²ASTM D470 BDOA = poly(tetramethylene adipate) glycol PDOA= poly(trimethylene adipate) glycol BDO = 1,4-butanediol PDO =1,3-propanediol

As can be seen from Table 1, the TPU samples made with poly(trimethyleneadipate) glycol did not bloom. However, the samples made utilizingpoly(tetramethylene adipate) glycol showed medium to heavy bloom afterbeing aged for only 3 months.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

1. A thermoplastic polyurethane which is comprised of the reactionproduct of (1) a hydroxyl terminated polyester intermediate, (2) apolyisocyanate, and (3) a glycol chain extender; wherein the hydroxylterminated polyester intermediate is comprised of repeat units that arederived from 1,3-propylene glycol and a dicarboxylic acid; wherein thehydroxyl terminated polyester intermediate has a number averagemolecular weight which is within the range of 500 to 10,000 Daltons; andwherein the thermoplastic polyurethane includes hard segments that arethe reaction product of the polyisocyanate and the glycol chainextender.
 2. The thermoplastic polyurethane specified in claim 1 wherein1,3-propylene glycol represents at least 70 weight percent of the glycolcomponent used in synthesizing the hydroxyl terminated polyesterintermediate.
 3. The thermoplastic polyurethane specified in claim 1wherein 1,3-propylene glycol represents at least 80 weight percent ofthe glycol component used in synthesizing the hydroxyl terminatedpolyester intermediate.
 4. The thermoplastic polyurethane specified inclaim 1 wherein 1,3-propylene glycol represents at least 90 weightpercent of the glycol component used in synthesizing the hydroxylterminated polyester intermediate.
 5. The thermoplastic polyurethanespecified in claim 1 wherein 1,3-propylene glycol represents at least 95weight percent of the glycol component used in synthesizing the hydroxylterminated polyester intermediate.
 6. The thermoplastic polyurethanespecified in claim 1 wherein the glycol component used in synthesizingthe hydroxyl terminated polyester intermediate consists essentially of1,3-propylene glycol.
 7. The thermoplastic polyurethane specified inclaim 2 wherein the dicarboxylic acid is of the formula:HOOC(CH₂)_(n)COOH, wherein n represents an integer within the range of 2to
 10. 8. The thermoplastic polyurethane specified in claim 3 whereinthe dicarboxylic acid is of the formula: HOOC(CH₂)_(n)COOH, wherein nrepresents an integer within the range of 4 to
 8. 9. The thermoplasticpolyurethane specified in claim 4 wherein the dicarboxylic acid isadipic acid.
 10. The thermoplastic polyurethane specified in claim 1wherein the hydroxyl terminated polyester intermediate ispoly(1,3-propylene adipate) glycol.
 11. The thermoplastic polyurethanespecified in claim 1 wherein glycol chain extender is selected from thegroup consisting of ethylene glycol, propylene glycol, 1,4-butaneglycol, 1,5-pentane diol, 1,6-hexane diol, and hydroquinonebis(2-hydroxyethyl)ether.
 12. The thermoplastic polyurethane specifiedin claim 1 wherein glycol chain extender is 1,4-butane diol.
 13. Thethermoplastic polyurethane specified in claim 1 wherein glycol chainextender is 1,3-propane diol.
 14. The thermoplastic polyurethanespecified in claim 1 wherein polyisocyanate is a diisocyanate.
 15. Thethermoplastic polyurethane specified in claim 1 wherein polyisocyanateis an aromatic diisocyanate.
 16. The thermoplastic polyurethanespecified in claim 15 wherein aromatic polyisocyanate is selected fromthe group consisting of 4,4′-methylene bis-(phenyl isocyanate), m-xylenediisocyanate, phenylene-1-4-diisocyanate, naphthalene-1,5-diisocyanate,diphenylmethane-3,3′-dimethoxy-4,4′-diisocyanate, and toluenediisocyanate.
 17. The thermoplastic polyurethane specified in claim 1wherein diisocyanate is an aliphatic diisocyanate selected from thegroup consisting of isophorone diisocyanate, 1,4-cyclohexyldiisocyanate, decane-1,10-diisocyanate,dicyclohexylmethane-4,4′-diisocyanate, and 1,6-hexane diisocyanate. 18.The thermoplastic polyurethane specified in claim 1 wherein the hydroxylterminated polyester intermediate is poly(1,3-propylene adipate) glycol,wherein the glycol chain extender is 1,4-butane diol, and wherein thepolyisocyanate is 4,4′-methylene bis-(phenyl isocyanate).
 19. Thethermoplastic polyurethane specified in claim 18 wherein the hydroxylterminated polyester intermediate has a number average molecular weightwhich is within the range of 1000 to 4000 Daltons.
 20. The thermoplasticpolyurethane specified in claim 19 wherein the thermoplasticpolyurethane has a weight average molecular weight of at least 100,000Daltons; and wherein the hard segments represent from 10 weight percentto 40 weight percent of the total weight of the thermoplasticpolyurethane.
 21. A process for manufacturing a molded article whichcomprises (a) heating a thermoplastic polyurethane composition to atemperature which is above the melting point of the thermoplasticpolyurethane composition, wherein the thermoplastic polyurethanecomposition is comprised of the thermoplastic polyurethane specified inclaim 1; (b) injecting the thermoplastic polyurethane composition into amold; (c) cooling the thermoplastic polyurethane composition in the moldto a temperature which is below the melting point of the thermoplasticpolyurethane composition to produce the molder article; and (d) removingthe molded article from the mold.
 22. A process for manufacturing anextruded article which comprises (a) heating a thermoplasticpolyurethane composition to a temperature which is above the meltingpoint of the thermoplastic polyurethane composition, wherein thethermoplastic polyurethane composition is the reaction product of (1) ahydroxyl terminated polyester intermediate, (2) a polyisocyanate, and(3) a glycol chain extender; wherein the hydroxyl terminated polyesterintermediate is comprised of repeat units that are derived from1,3-propylene glycol and a dicarboxylic acid; wherein the hydroxylterminated polyester intermediate has a number average molecular weightwhich is within the range of 500 to 10,000 Daltons; and wherein thethermoplastic polyurethane includes hard segments that are the reactionproduct of the polyisocyanate and the glycol chain extender; (b)extruding the thermoplastic polyurethane composition into the desiredshape of the extruded article; and (c) cooling the thermoplasticpolyurethane composition to a temperature which is below the meltingpoint of the thermoplastic polyurethane composition to produce theextruded article.
 23. A process as specified in claim 22 wherein theextruded article is a clear film.
 24. A process as specified in claim 22wherein the extruded article is a clear tube.
 25. A clear film which iscomprised of the thermoplastic urethane specified in claim
 1. 26. Aclear tube which is comprised of the thermoplastic urethane specified inclaim
 1. 27. A shoe having an upper and a sole, wherein the sole iscomprised of the thermoplastic urethane specified in claim 1.